1. Field of the Invention
The present invention relates to a trigger switch and, more particularly, to improvements in a switch structure inside a trigger switch used in an electric power tool.
2. Prior Art
A conventional and known trigger switch is disclosed, for example, in JP-A-2003-109451. This trigger switch has a control device that is mounted to a case by an improved mounting mechanism. An attempt has been made to reduce the thickness while securing good dustproofness. To achieve this, the state of the switch mechanism inside the case of the trigger switch is switched based on a triggering manipulation. The switch mechanism is incorporated in the internal space of the case. The opening at one side of the case that is opened in a corresponding manner to the internal space of the case is covered and closed by a cover. The control device is accommodated in a concave accommodation portion formed in a part of the other side surface of the case. The other side surface of the case including the outer surface of the control device is covered by a heat-dissipating plate to form an integrated structure.
However, in this conventional trigger switch, when a movable contact element moving swingably is mounted to a support member, the contact element is simply placed on the support member to permit the contact member to swing. Consequently, there is such a problem that the contact element comes off from the support member during use. Furthermore, when the movable contact element moves, the support member tends to bound, producing an arc across the contacted portion. This would produce poor contact. To prevent this, it is necessary to add a brush. However, to hold the brush, a process for tightening the brush is required. This produces a problem that the cost is increased.
Furthermore, as shown in FIG. 26, a trigger 120 is normally molded from resin. Therefore, opening portions are formed only from one direction. Utilizing the opening portions, trigger guide ribs 121 are attached from other components. Therefore, whenever the trigger 120 moves, dust 123 accumulates in the opening portions, 122. The accumulated dust 123 is stored in the interiors of the opening portions 122. The dust stays there without being discharged and interferes with the trigger guide ribs 121. Under this condition, the trigger cannot be pulled to its full stroke, thus presenting a problem.
To permit the trigger to be mounted in an electric power tool easily, the switch itself is required to be integrated with the control device (FET). Therefore, an opening portion is formed in the cover of the switch, and the control device is disposed in the opening portion. In spite of this contrivance, a problem takes place. The movable contact element is received in a position adjacent to the opening portion. Because the opening portion is formed in a part of the cover, dust intruding from the opening portion reaches the chamber of the switch mechanism where the movable contact element is mounted. To prevent this problem, dustproof rubber is used in or around the opening portion in the cover as a dustproof countermeasure. Consequently, intrusion of dust can be prevented. However, there is the problem that dedicated packing or the like is necessary, increasing the cost.
Furthermore, the conventional product has the problem that heat from the FET stays inside the switch because the switch mechanism and the portion accommodating the FET are integrated.